The present invention relates in general to models employed in restorative or prosthetic dentistry, and more particularly to a pin fixed in a removable die of a model and received by a base to which the model is received.
In the making of a fixed dental prosthesis (i.e. gold and ceramic crown or bridge) it is required that an accurate replica of the existing teeth and gums (dentition) be made. The replicas, herein referred to as models, are made by taking an impression of dentition. Material capable of adapting to the exact shape and dimension of the dentition are, for example, silicon, rubber and agar hydrocolloid. The impression is a "negative" model in which plaster, such as calcium sulfatehemihydrate, is poured. Upon removal from the impression, the plaster forms the model on which the prosthesis is constructed. The model is secured to a base of the plaster to increase its overall strength.
The plaster model comprises teeth which are replicas of the teeth remaining in the mouth of the patient and a replica of the teeth to be prepared by prosthetic or restorative dentistry. It is the teeth prepared for the prosthesis to be developed by restorative dentistry that requires a pin.
The replica of the teeth to be prepared by prosthetic or restorative dentistry is known as a die. It is desired in restorative dentistry that the die be removable and replaceable in the model. The die should be returned to the model in an exact position. Additionally, the die should not be susceptible to rotation about the pin. During fabrication of the prosthesis, the pin should be able to withstand torque stresses applied to the die. Should the tip of the pin fracture because of torque stresses, then the pin should be able to be repaired and restored with facility and ease of operation.
Additionally, the pin should be constructed to obviate the need for depressions in the wall of the die confronting the model. Furthermore, the tip of the pin should be constructed to fit into the narrow lower mouth anterior teeth depression (labiel-lingual). The opening in the base formed to receive the pin should be able to be cleaned with facility and ease of operation should debris, foreign matter, burrs or stones be deposited therein. Debris and foreign matter in the opening of the base detracts from the accurate seating of the shank of the pin in the opening of the base during the replacement of the die in the model.
Heretofore, dowel pins have been employed for indexing a removable die of a model. Such dowel pins have generally been made of brass. The dowel pins were fixed in the die and extended therefrom to be received by a suitable opening in the base. The dowel pins serve to index and locate the die relative to the model. Typically, the dowel pin had a cylindrical configuration or a surface equidistance from the axis of the pin. At times, a portion of the cylindrical surface would have a flat taper portion extending in the axial direction equidistance from the axis thereof.
Customarily, the dowel pin had a knurled end for retention in the die. In some instances, an adhesive, such as cyano acrylate ester, on a smooth surface was employed to secure the dowel pin in the die. At other times, the dowel pin had a stem with flat sides for retention in the die.
Additionally, the dies heretofore employed had two dowel pins extending from the die. Some dowel pins used sleeves for improved accuracy in indexing the die in the model. The sleeve may have facilitated the removal of the die from the model.
In the patent to Lystager U.S. Pat. No. 3,704,519, issued on Dec. 5, 1972, for Method To Prepare A Dental Model, there is disclosed a die with a pair of spaced pins embedded therein. Bushings are disposed in the base for receiving the pins. The patent to Cooper U.S. Pat. No. 3,286,350, issued Nov. 22, 1966, for Dowel And Clip Assembly And Its Use In The Manufacture Of Dental Restorations discloses a pin embedded in a die that is received by a rubber core embedded in the base. The shank of the pin is undercut to rest on the top wall of a spring clip, which is also embedded in the base. As for the patent to Spalten U.S. Pat. No. 3,226,827, issued on Jan. 4, 1966, for Dental Apparatus, there is shown a dowel pin with a tip having flat walls. The patent to Weissman U.S. Pat. No. 3,153,283 and the patent to Susman et al. U.S. Pat. No. 3,518,761, disclose pins received by sleeves.
The patent to Bailey U.S. Pat. No. 1,867,300, issued on July 12, 1932, for Metallic Socket And Mold For Amalgam Dies shows a socket receiving the shank of a die, while the patent to Spalten et al. U.S. Pat. No. 2,851,728, issued on Sept. 16, 1958, for Interlockable Dental Pin And Repositioning Gauge And Method Of Using discloses a stem for a pin having trapezoidal cross-sectional areas. Another patent of interest is the patent to Waltke U.S. Pat. No. 3,453,736, issued on July 8, 1969, for Dowels For Fireable Ceramic Dies And Method For Their Use, which shows dowels of various configurations. Another patent of interest is the patent to Stengel U.S. Pat. No. 3,478,428, issued on Nov. 18, 1969, for Apparatus For Dental Models.